RISC OS advocate Paul Vigay, whose body was found off the coast of Portsmouth last year, left behind a list of his passwords and a note to his girlfriend saying "I love you", an inquest has heard.

ISP owner and crop circle researcher Paul, 44, had split with his girlfriend Andrea Louie Smith on the night of his death and was £10,000 in debt. His body was discovered in the sea in February 2009; reports showed there was no suspicious circumstances, no suicide note and no sign of struggle on Paul's body, and that he had only consumed a small quantity of alcohol. There was no CCTV footage or witnesses to the death, leading a coroner to admit that his death will remain a mystery.

The hearing, held in Portsmouth, heard that Louie and Paul had fallen out over his decision to let one of his friends stay at their house, and that she had wanted to wed and bring up a family.

Louie, who published the magazine RISC OS Now with Paul, told the inquest that she had discussed ending their three-year relationship during a meal a week before Paul's death. She said: "It was not arguing. It was not aggressive. It was just emotional. He was crying, I was crying. I said 'this is it. I think it's come to the end of the line now'."

On the night of his death, as Louie packed her bags to leave, Paul said he was going outside. Louie told the inquest: "I said, 'You promise me you come home.' He said: 'It's not important now'."

The passwords Paul left in a note did not work when the police and Paul's family attempted to use them.

Paul's father, John, told the inquest: "He had very firm beliefs and he would stick to them. He did not believe in suicide."

Coroner David Horsley, who recorded an open verdict, said: "I cannot say beyond reasonable doubt that yes Paul has taken his own life. "The only person who could tell us what was going on in his mind and what happened that night is sadly not here to tell us."

Paul, of Manners Road, Southsea, was a keen RISC OS advocate and, as well as developing numerous pieces of software for the platform, he also ran the riscos.org website and was well known for helping users solve computing problems on mailing lists and other online forums. Stunned by news of his death, RISC OS users, crop circle investigators and his personal friends joined together in paying moving tributes to Paul in mailing list and newsgroup messages and in posts on an online book of condolence.